Patent GB-781026-A (GB)
Title: Improvements in and relating to electric sequencing control systems
Filed: 1955-06-14
Abstract: 781,026. Supply systems for resistance welders. GENERAL ELECTRIC CO. June 14, 1955 [June 14, 1954], No. 17135/55. Class 38 (4). A cycle of operations for a welding machine is initiated by closing switch 44 to fire valve 26 and to energize operating coil 28 of a solenoid valve for moving the welding electrodes into engagement with the work. A transformer 43 is energized to charge capacitor 49 so that the potential developed across resistor 52 maintains the valve 26 conductive and allows release of the switch 44 without discontinuing the cycle. A capacitor 37 is simultaneously charged from secondary winding 43b of the transformer 43 whereby valve 36 is fired and capacitor 24 is discharged through adjustable resistor 56. At the end of the discharge period, the valve 20 is rendered conductive to charge capacitors 11, 12, and to initiate conduction of the valve 3 so that the primary winding 1b of transformer 1 is energized and secondary winding 1a supplies impulses to an ignition firing circuit which, through a welding transformer, applies current to the electrodes. The voltage induced in secondary winding 1d charges capacitor 57 to terminate conduction of valve 20 at the end of its first halfcycle, and, consequently, capacitor 12 begins to discharge through adjustable resistor 16 into capacitor 11, whereby the control potential of valve 3 decreases in accordance with the discharge rate of the capacitor 12. During this discharge period valves 3 and 4 conduct on alternate half-cycles of the line voltage and cause the main ignitrons to furnish welding current pulses to the electrodes, the passage of current through the leading timing valve 3 initiating conduction of the trailing valve 4 which energizes transformer 2 for firing the trailing main ignition. The discharge of valve 3 provides a maintaining circuit independent of the valve 26 for the solenoid 28 through rectifiers 31, 32 and also energizes transformer 42 to charge capacitor 59. As a result, valve 26 is shut-off to de-energize transformer 43 and allow transformer 41 to charge capacitor 55, so rendering valve 27 conductive. The deenergization of transformer 43 also causes discharge of capacitor 37 and, after a period, the valve 36 is shut-off, the energization of transformer 41 being maintained, however by a parallel circuit through rectifier 33 and valve 3. When the capacitor 12 has discharged, valves 3, 4 become non-conductive to terminate the first heating period of the welding electrodes and to initiate a cooling period followed by a second heating period. Premature de-energization of the solenoid 28 is prevented by means of valve 27 and rectifier 31. Capacitor 57 discharges through adjustable resistor 63 until, after a predetermined interval, valve 20 restrikes and the timing valves 3, 4 are again rendered conductive to initiate the second heating period. This period is terminated when the capacitor 12 is again discharged, transformer 41 being de-energized to initiate discharge of capacitor 55, whereby, after a period of delay, valve 27 is shut-off and solenoid 28 is de-energized to permit separation of the welding electrodes. Transformer 42 is also de-energized and capacitor 59 discharges to prevent firing of the valve 26 until the end of the discharge period during which a new cycle of operation cannot be started although the switch 44 may be closed.